Tailoring of resins, such as polyethylene homopolymer or copolymer resins, is a well-known method of altering the molecular architecture and thus the bulk properties of the resin and of films and articles made therefrom. Tailoring involves treating the resin with an agent, such as a peroxide or oxygen, capable of controlled degradation of the resin. The effect of tailoring on the resin rheological properties can be seen in an increase in shear thinning behavior, an increase in elasticity, an increase in melt tension, a reduction in swelling during blow molding, and an increase in bubble stability film blowing. Although not wishing to be bound by theory, it is believed that an effect of tailoring is to introduce low levels of long chain branching in the resin.
A particularly useful application for polyethylene resins is in films. The gauge uniformity of films, particularly films of medium density polyethylene (MDPE) and high density polyethylene (HDPE) resins, frequently is not adequate for producing the thin films required for many applications. Attempts have been made to tailor polyethylene resins to improve resin or film properties; see, e.g., European Patent Publication No. EP 0 457 441, and U.S. Pat. Nos. 5,728,335; 5,739,266; and 6,147,167. However, it would be desirable to have improved methods of extruding polyethylene, particularly pelletized medium or high density polyethylene film resin, to provide resins having improved gauge uniformity when processed into film.